This invention is directed to multi-phase polyblends of polyamide resins, high molecular weight thermoplastic copolymers containing unsaturated carboxylic acid, and adducts of carboxylic acid anhydrides and elastomeric polymers. The invention additionally relates to a method for the preparation of such thermoplastic moldable polymer blends wherein chemical grafting of the blend components is accomplished.
Polyamide resins have been widely used as thermoplastics in molding applications because of their high resistance to chemicals, heat, and abrasion and their generally good mechanical properties. However, polyamide resins possess certain deficiencies, including shrinkage during molding and high hygroscopicity. The tendency to absorb water results in dimensional stability problems and loss of mechanical strength. Although polyamide resins are fairly tough under most impact conditions, they can be notch-sensitive and brittle at low temperatures. Polyamide resins have been blended with other polymers to compensate for these deficiencies or to enhance mechanical properties such as stiffness and tensile strength.
U.S. Pat. No. 4,528,326 teaches polyblends of polyamide resins having at least seven methylene units separating each amide functional group and rubber-modified styrene/unsaturated carboxylic acid anhydride or imide copolymer resins. Polyblends of polyamides containing fewer than seven methylene units were found to have undesirably low impact strength.
Jpn. Pat. No. 56-112957 teaches polyblends of polyamide resins and rubber-modified styrene copolymer containing high levels of unsaturated carboxylic acid anhydride, with the styrene copolymer preferably also containing an unsaturated carboxylic acid ester in order to minimize the extent of undesired cross-linking during melt-kneading.
U.S. Pat. No. 4,421,892 contains similar teachings regarding polyblends of polyamide resins and styrene copolymers containing high levels of unsaturated carboxylic acid anhydride. Good mechanical strength was only achieved in such polyblends when an unsaturated carboxylic acid ester was additionally present in the styrene copolymer.
Jpn. Pat. No. 57-025355 teaches blends of styrene/maleic anhydride copolymers and polyamides, but does not teach how adequate impact properties may be accomplished with such blends.
Ger. Pat. No. 3,604,348 teaches blends of polyamides, ethylene/acrylate or acrylic acid copolymers, and styrene/acrylic acid or styrene/anhydride copolymers. Similar teachings are found in Ger. Pat. No. 3,604,376 which additionally discloses the use of a conjugated diene polymer or copolymer to improve the impact strength of such blends.
U.S. Pat. No. 4,174,358 teaches the toughening of polyamides by blending with elastomeric polymers bearing functional groups, including anhydride, which may chemically react with the polyamide so as to achieve grafting between the components.
U.S. Pat. No. 4,427,828 teaches the impact modification of polyamides with maleic anhydride adducts of either a hydrogenated polymer of a conjugated diene or a hydrogenated block or random copolymer of a copolymer of a conjugated diene and a monovinyl aromatic monomer.